Wireless power transmission device

Abstract

This wireless power transmission device comprises a first power transmission coil (2411), a second power transmission coil (2421), a first power transmission resonance circuit (241), a second power transmission resonance circuit (242), a first power conversion circuit (231), a second power conversion circuit (232), a first switching control circuit (221), and a second switching control circuit (222). The first power transmission resonance circuit (241) is configured using the first power transmission coil (2411) and a first power transmission resonance capacitor (2412). The second power transmission resonance circuit (242) is configured using a second power transmission coil (2421) and a second power transmission resonance capacitor (2422). The first power conversion circuit (231) converts an input DC voltage into an AC current through a switching operation and causes the AC current to flow to the first power transmission coil. The second power conversion circuit (232) converts an input DC voltage into an AC current through a switching operation and causes the AC current to flow to the second power transmission coil. The first switching control circuit (221) controls the switching operation of the first power conversion circuit (231). The second switching control circuit (222) controls the switching operation of the second power conversion circuit (232). The first switching control circuit (221) and the second switching control circuit (222) perform power transmission control such that the phase of the first AC current flowing through the first power transmission coil (2411) and the phase of the second AC current flowing through the second power transmission coil (2421) have opposite phases. The first power transmission capacitor (2412) and the second power transmission capacitor (2422) set the respective capacitance values so that at the switching frequency, the input impedance as viewed from the load side where the wireless power transmission device supplies power via the first power transmission coil (2411) and the second power transmission coil (2421) is in the vicinity of a minimum.

Description

Wireless power transmission device

[0001] The present invention relates to a power transmission control technique for a wireless power transmitter used in a wireless power supply system.

[0002] Wireless power transfer technology can eliminate the need for a charging connector as a method of powering electronic devices and charging secondary batteries installed in electronic devices. Because there is no need for an electrical connection terminal, there is no problem with corrosion or deterioration of metal terminals, and waterproofing is improved.

[0003] As an example of such wireless power supply, Patent Documents 1 to 3 describe wireless power supply systems using a plurality of power transmission coils.

[0004] Japanese Patent No. 6750456 Japanese Patent Publication No. 2016-5393 Japanese Patent No. 6240311

[0005] For example, electronic devices such as wireless earphones and hearing aids require two devices with a power receiving function, so a wireless power transfer system may be configured using two power transmitting coils and two power receiving coils.

[0006] However, as the number of power transmitting coils and power receiving coils increases, radiation noise and leakage electromagnetic fields become larger, causing problems.

[0007] Therefore, an object of the present invention is to suppress radiation noise and leakage electromagnetic fields in a wireless power transmission device that requires multiple power transmission coils.

[0008] A wireless power transmitter according to one embodiment of the present invention includes a first power transmitting coil, a second power transmitting coil, a first power transmitting resonant circuit, a second power transmitting resonant circuit, a first power conversion circuit, a second power conversion circuit, a first switching control circuit, and a second switching control circuit. The first power transmitting resonant circuit is configured using a first power transmitting coil and a first power transmitting resonant capacitor. The second power transmitting resonant circuit is configured using a second power transmitting coil and a second power transmitting resonant capacitor. The first power conversion circuit converts an input DC voltage into an AC current by switching operation and passes the AC current to the first power transmitting coil. The second power conversion circuit converts the input DC voltage into an AC current by switching operation and passes the AC current to the second power transmitting coil. The first switching control circuit controls the switching operation of the first power conversion circuit. The second switching control circuit controls the switching operation of the second power conversion circuit.

[0009] The first switching control circuit and the second switching control circuit perform power transmission control so that the phase of the first AC current flowing through the first power transmitting coil and the phase of the second AC current flowing through the second power transmitting coil are opposite in phase. The first power transmitting resonant capacitor and the second power transmitting resonant capacitor are set to have capacitance values ​​such that, at a switching frequency, the input impedance seen from the first power transmitting coil and the second power transmitting coil to the load to which the wireless power transmitter supplies power is near a minimum. A first electromagnetic resonant field by the first power transmitting coil and a second electromagnetic resonant field by the second power transmitting coil are individually formed. In a near-field where the distance from the first power transmitting coil and the second power transmitting coil is short, the first power transmitting coil and the second power transmitting coil are arranged at a distance to suppress electromagnetic interference between them. In a far-field where the distance from the first power transmitting coil and the second power transmitting coil is long, the electromagnetic waves generated by the first power transmitting coil and the electromagnetic field generated by the second power transmitting coil cancel each other out.

[0010] In this configuration, the electromagnetic field generated by the first power transmitting coil and the electromagnetic field generated by the second power transmitting coil are out of phase with each other. As a result, in the near field, the leakage magnetic flux of the first power transmitting coil and the leakage magnetic flux of the second power transmitting coil cancel each other out, thereby suppressing electromagnetic interference between the first power transmitting coil and the second power transmitting coil. Furthermore, in the far field, the electromagnetic waves generated by the first power transmitting coil and the electromagnetic waves generated by the second power transmitting coil cancel each other out, thereby suppressing the leakage electromagnetic field.

[0011] Furthermore, by setting the capacitance values ​​of the first and second power transmission coils so that the input impedance seen from the load side is close to a minimum, a decrease in power supply efficiency is suppressed.

[0012] According to the present invention, radiation noise and leakage electromagnetic fields can be suppressed in a wireless power transmitting device including a plurality of power transmitting coils.

[0013] FIG. 1 is an equivalent circuit diagram of a wireless power supply system apparatus according to a first embodiment of the present invention. FIGS. 2A and 2B are diagrams showing an example of the state of a magnetic field in the near field of a power transmitting coil and a power receiving coil at a certain timing. FIG. 3 is a diagram showing an example of the state of an electromagnetic field in the far field of two power transmitting coils. FIG. 4A is a graph showing an example of the relationship between frequency and input impedance. FIG. 4B is a graph showing an example of the relationship between frequency and voltage gain. FIG. 5 is a graph showing an example of the relationship between the distance between a first power transmitting coil and a second power transmitting coil and a coupling coefficient. FIG. 6 is an equivalent circuit diagram of a wireless power supply system apparatus according to a second embodiment of the present invention. FIG. 7 is an equivalent circuit diagram of a wireless power supply system apparatus according to a third embodiment of the present invention.

[0014] [First embodiment] A wireless power supply system apparatus according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is an equivalent circuit diagram of the wireless power supply system apparatus according to the first embodiment of the present invention.

[0015] (Schematic Configuration of Wireless Power Supply System Apparatus 10) As shown in FIG. 1, the wireless power supply system apparatus 10 includes a power transmitting apparatus 20 and a power receiving apparatus 30.

[0016] The power transmission device 20 and the power receiving device 30 are physically separate entities. The power receiving device 30 includes a first power receiving device 31 and a second power receiving device 32. The first power receiving device 31 and the second power receiving device 32 are physically separate entities. Note that the first power receiving device 31 and the second power receiving device 32 may be connected in a state in which their positional relationship is changeable.

[0017] An example of an application of the power receiving device 30 is a wireless earphone. The power transmitting device 20 is a charging device for the wireless earphone. When the power receiving device 30 is a wireless earphone, for example, the first power receiving device 31 is a wireless earphone for the right ear, and the second power receiving device 32 is a wireless earphone for the left ear.

[0018] The wireless earphone is just one example, and the configuration according to the embodiment of the present invention can be applied to any power receiving device that is configured from a plurality of individual power receiving devices.

[0019] (Power Transmitter 20) The power transmitter 20 includes an MCU 21, a first switching control circuit 221, a second switching control circuit 222, a first power conversion circuit 231, a second power conversion circuit 232, a first power transmitter resonant circuit 241, and a second power transmitter resonant circuit 242.

[0020] The first power conversion circuit 231 includes a switching element S1H and a switching element S1L. The second power conversion circuit 232 includes a switching element S2H and a switching element S2L. The switching elements S1H, S1L, S2H, and S2L are configured using power semiconductors.

[0021] The first power transmitting resonant circuit 241 includes a first power transmitting coil 2411 and a first power transmitting resonant capacitor 2412. The first power transmitting coil 2411 and the first power transmitting resonant capacitor 2412 are connected in series to form a first power transmitting series resonant circuit.

[0022] The second power transmitting resonant circuit 242 includes a second power transmitting coil 2421 and a second power transmitting resonant capacitor 2422. The second power transmitting coil 2421 and the second power transmitting resonant capacitor 2422 are connected in series to form a second power transmitting series resonant circuit.

[0023] The first power transmitting coil 2411 and the second power transmitting coil 2421 are configured by loop-shaped conductors. The first power transmitting coil 2411 and the second power transmitting coil 2421 have the same shape. In other words, the first power transmitting coil 2411 and the second power transmitting coil 2421 have the same size.

[0024] The capacitance value of the first power transmitting resonant capacitor 2412 is the same as the capacitance value of the second power transmitting resonant capacitor 2422. As a result, the resonant frequency of the first power transmitting resonant circuit 241 is the same as the resonant frequency of the second power transmitting resonant circuit 242. This resonant frequency is set to the natural resonant frequency fr of the wireless power supply system apparatus 10.

[0025] The first power conversion circuit 231 and the second power conversion circuit 232 are connected in parallel to a DC power supply. The DC power supply has a positive electrode and a negative electrode, and the negative electrode is connected to a reference potential. The DC power supply may be included in the power transmission device 20 as shown in FIG. 1 , or may be separate from the power transmission device 20. Note that the power transmission device 20 may include an input capacitor connected in parallel to the DC power supply.

[0026] The drain terminal of the switching element S1H of the first power conversion circuit 231 is connected to the positive electrode of the DC power supply. The source terminal of the switching element S1H is connected to the drain terminal of the switching element S1L. The source terminal of the switching element S1L is connected to the negative electrode of the DC power supply.

[0027] The drain terminal of the switching element S2H of the second power conversion circuit 232 is connected to the positive electrode of the DC power supply. The source terminal of the switching element S2H is connected to the drain terminal of the switching element S2L. The source terminal of the switching element S2L ​​is connected to the negative electrode of the DC power supply.

[0028] A node between the source terminal of the switching element S1H and the drain terminal of the switching element S1L of the first power conversion circuit 231 is connected to one terminal of the first power transmitting resonant circuit 241. The other terminal of the first power transmitting resonant circuit 241 is connected to the source terminal of the switching element S1L.

[0029] A node between the source terminal of the switching element S2H and the drain terminal of the switching element S2L ​​of the second power conversion circuit 232 is connected to one terminal of the second power transmitting resonant circuit 242. The other terminal of the second power transmitting resonant circuit 242 is connected to the source terminal of the switching element S2L.

[0030] The MCU 21, the first switching control circuit 221, and the second switching control circuit 222 are connected to a DC power supply.

[0031] The MCU 21 is connected to an input terminal of the first switching control circuit 221 and an input terminal of the second switching control circuit 222. An output terminal of the first switching control circuit 221 is connected to a gate terminal of the switching element S1H and a gate terminal of the switching element S1L of the first power conversion circuit 231. An output terminal of the second switching control circuit 222 is connected to a gate terminal of the switching element S2H and a gate terminal of the switching element S2L ​​of the second power conversion circuit 232.

[0032] In the above description, the power transmitting device 20 has all of the above-described functional units housed in a single housing. However, the power transmitting device 20 may be configured with a first device and a second device that are configured separately. The first device includes a first switching control circuit 221, a first power conversion circuit 231, and a first power transmitting resonant circuit 241. The second device includes a second switching control circuit 222, a second power conversion circuit 232, and a second power transmitting resonant circuit 242. The MCU 21 may be provided in either the first device or the second device, or may be provided separately.

[0033] (Power Receiving Device 30 ) The power receiving device 30 includes a first power receiving device 31 and a second power receiving device 32 .

[0034] The first power receiving device 31 includes a first power receiving resonant circuit 311, a first power receiving rectifying circuit 321, a first power receiving smoothing circuit 331, and a load 341. The first power receiving smoothing circuit 331 is configured by a smoothing capacitor.

[0035] The first power receiving resonant circuit 311 includes a first power receiving coil 3111 and a first power receiving resonant capacitor 3112. The first power receiving coil 3111 and the first power receiving resonant capacitor 3112 are connected in parallel to form a first power receiving parallel resonant circuit. An output terminal of the first power receiving resonant circuit 311 is connected to an input terminal of the first power receiving rectifier circuit 321.

[0036] A first power receiving smoothing circuit 331 is connected in parallel to the output terminal of the first power receiving rectifying circuit 321. Both ends of the first power receiving smoothing circuit 331 are connected to a load 341.

[0037] The second power receiving device 32 includes a second power receiving resonant circuit 312, a second power receiving rectifying circuit 322, a second power receiving smoothing circuit 332, and a load 342. The second power receiving smoothing circuit 332 is configured by a smoothing capacitor.

[0038] The second power receiving resonant circuit 312 includes a second power receiving coil 3121 and a second power receiving resonant capacitor 3122. The second power receiving coil 3121 and the second power receiving resonant capacitor 3122 are connected in parallel to form a second power receiving parallel resonant circuit. An output terminal of the second power receiving resonant circuit 312 is connected to an input terminal of the second power receiving rectifier circuit 322.

[0039] A second power receiving smoothing circuit 332 is connected in parallel to the output terminal of the second power receiving rectifying circuit 322. Both ends of the second power receiving smoothing circuit 332 are connected to a load 342.

[0040] The first power receiving coil 3111 and the second power receiving coil 3121 are configured with loop-shaped conductors. The first power receiving coil 3111 and the second power receiving coil 3121 have the same shape. In other words, the first power receiving coil 3111 and the second power receiving coil 3121 have the same size.

[0041] The capacitance value of the first power receiving resonant capacitor 3112 is the same as the capacitance value of the second power receiving resonant capacitor 3122. As a result, the resonant frequency of the first power receiving resonant circuit 311 is the same as the resonant frequency of the second power receiving resonant circuit 312. This resonant frequency is set to the natural resonant frequency fr of the wireless power supply system apparatus 10.

[0042] (Wireless Power Supply) The MCU 21 sets a power transmission control signal so as to supply a desired DC current to the load 341 and the load 342. The MCU 21 outputs the power transmission control signal to the first switching control circuit 221 and the second switching control circuit 222.

[0043] Based on the power transmission control signal, the first switching control circuit 221 generates a first switching control signal that controls the switching operations of the switching elements S1H and S1L of the first power conversion circuit 231. The first switching control circuit 221 outputs the first switching control signal to the switching elements S1H and S1L.

[0044] When the first switching control signal is input, the switching elements S1H and S1L are alternately turned on (conducting) and off (open) at a predetermined switching frequency based on the first switching control signal.

[0045] As a result, the first power conversion circuit 231 made up of the switching element S1 H and the switching element S1 L converts the input DC voltage into AC current by switching operation, and passes the AC current to the first power transmitting coil 2411 of the first power transmitting resonant circuit 241 .

[0046] When the power receiving device 30 is placed at a predetermined position relative to the power transmitting device 20, the first power transmitting coil 2411 and the first power receiving coil 3111 are in a positional relationship that allows electromagnetic field coupling between them.

[0047] The first power receiving coil 3111 is coupled to the alternating magnetic field generated by the first power transmitting coil 2411 and generates an AC current. The first power receiving rectifier circuit 321 rectifies the AC current output from the first power receiving coil 3111 (first power receiving resonant circuit 311). The first power receiving smoothing circuit 331 smoothes the rectified current (rectified voltage) and outputs a DC current (DC voltage) to the load 341.

[0048] As a result, the desired DC power is supplied to the load 341 .

[0049] Based on the power transmission control signal, the second switching control circuit 222 generates a second switching control signal that controls the switching operations of the switching elements S2H and S2L of the second power conversion circuit 232. The second switching control circuit 222 outputs the second switching control signal to the switching elements S2H and S2L.

[0050] When the second switching control signal is input, the switching elements S2H and S2L are alternately turned on (conducting) and off (open) at a predetermined switching frequency based on the second switching control signal.

[0051] As a result, the second power conversion circuit 232 made up of the switching element S2H and the switching element S2L ​​converts the input DC voltage into AC current by switching operation and passes the AC current to the second power transmitting coil 2421 of the second power transmitting resonant circuit 242.

[0052] When the power receiving device 30 is placed at a predetermined position relative to the power transmitting device 20, the second power transmitting coil 2421 and the second power receiving coil 3121 are in a positional relationship that allows electromagnetic field coupling between them.

[0053] The second power receiving coil 3121 is coupled to the alternating magnetic field generated by the second power transmitting coil 2421 and generates an AC current. The second power receiving rectifier circuit 322 rectifies the AC current output from the second power receiving coil 3121 (second power receiving resonant circuit 312). The second power receiving smoothing circuit 332 smoothes the rectified current (rectified voltage) and outputs a DC current (DC voltage) to the load 342.

[0054] As a result, the desired DC power is supplied to the load 342 .

[0055] In this way, the wireless power supply system apparatus 10 can simultaneously supply power from the power transmitting device 20 to the load 341 of the first power receiving device 31 and the load 342 of the second power receiving device 32 .

[0056] Here, the capacitance of the first power transmitting resonant capacitor 2412 is set so that the input impedance seen from the first power conversion circuit 231 to the load 341 side is close to a minimum at the switching frequency of the first power conversion circuit 231 .

[0057] By setting the capacitance of the first power transmitting resonant capacitor 2412 in this manner, the switching frequency of the first power conversion circuit 231 approximately matches the resonant frequency of the first power transmitting resonant circuit 241 and the resonant frequency of the first power transmitting coil 2411 and the first power receiving coil 3111.

[0058] As will be described in detail later, this resonant frequency varies depending on the degree of coupling (degree of electromagnetic field coupling) between the first power transmitting coil 2411 and the first power receiving coil 3111, and may or may not be the same as the natural resonant frequency fr. Therefore, the frequency at which the input impedance is minimum varies depending on the degree of electromagnetic field coupling, and the capacitance of the first power transmitting resonant capacitor 2412 is set in response to this change.

[0059] In this case, it is preferable that the capacitance of the first power receiving resonant capacitor 3112 is set to be approximately the same as the capacitance of the first power transmitting resonant capacitor 2412 and that they match.

[0060] As a result, the first power transmitting coil 2411 and the first power receiving coil 3111 form a first magnetic field resonance coupling and form a first electromagnetic field resonance field. Therefore, the wireless power supply system apparatus 10 can supply power from the power transmitting device 20 to the first power receiving device 31 with low loss.

[0061] The capacitance of the second power transmitting resonant capacitor 2422 is set so that the input impedance seen from the second power conversion circuit 232 toward the load 342 is close to a minimum at the switching frequency of the second power conversion circuit 232. The switching frequency of the second power conversion circuit 232 is set to be the same as the switching frequency of the first power conversion circuit 231.

[0062] By setting the capacitance of the second power transmitting resonant capacitor 2422 in this manner, the switching frequency of the second power conversion circuit 232 approximately matches the resonant frequency of the second power transmitting resonant circuit 242 and the resonant frequency of the second power transmitting coil 2421 and the second power receiving coil 3121.

[0063] As will be described in detail later, this resonant frequency varies depending on the degree of coupling (degree of electromagnetic field coupling) between the second power transmitting coil 2421 and the second power receiving coil 3121, and may or may not be the same as the natural resonant frequency fr. Therefore, the frequency at which the input impedance is minimum varies depending on the degree of electromagnetic field coupling, and the capacitance of the second power transmitting resonant capacitor 2422 is set in response to this change.

[0064] In this case, it is preferable that the capacitance of the second power receiving resonant capacitor 3122 is set to be approximately the same as the capacitance of the second power transmitting resonant capacitor 2422 and that they match.

[0065] As a result, the second power transmitting coil 2421 and the second power receiving coil 3121 form a second magnetic field resonance coupling and form a second electromagnetic field resonance field. Therefore, the wireless power supply system apparatus 10 can supply power from the power transmitting device 20 to the second power receiving device 32 with low loss.

[0066] In this way, the wireless power supply system apparatus 10 can supply power from the power transmitting apparatus 20 to the first power receiving apparatus 31 and the second power receiving apparatus 32 simultaneously with low loss.

[0067] At this time, in the wireless power supply system apparatus 10, the first power transmitting coil 2411 and the first power receiving coil 3111 form a first electromagnetic resonant field, and the second power transmitting coil 2421 and the second power receiving coil 3121 form a second electromagnetic resonant field.

[0068] As a result, the wireless power supply system apparatus 10 can supply power more reliably and stably than wireless power supply using simple magnetic field coupling, even if the distance between the first power transmitting coil 2411 and the first power receiving coil 3111 and the distance between the second power transmitting coil 2421 and the second power receiving coil 3121 is long (even if the power transmitting coil and the power receiving coil are far apart).The wireless power supply system apparatus 10 can supply power with low loss depending on the distance.

[0069] In this configuration, the wireless power supply system apparatus 10 further executes the following phase control.

[0070] Specifically, the first switching control circuit 221 and the second switching control circuit 222 are set so that the AC current (first AC current) flowing through the first power transmission coil 2411 and the AC current (second AC current) flowing through the second power transmission coil 2421 are in opposite phases.

[0071] This can be set, for example, by inverting the on / off of the first switching control signal of the first switching control circuit 221 and the on / off of the second switching control signal of the second switching control circuit 222. Alternatively, it can be set based on the power transmission control signal from the MCU 21, for example.

[0072] In this way, by making the phase of the first AC current and the phase of the second AC current opposite to each other, the following effects can be obtained.

[0073] 2A and 2B are diagrams showing an example of the state of the magnetic field in the near field of the power transmitting coil and the power receiving coil at a certain timing. Fig. 2A shows a case where the first power transmitting current it1 and the first power receiving current ir1 are in phase, and the second power transmitting current it2 and the second power receiving current ir2 are in phase. Fig. 2B shows a case where the first power transmitting current it1 and the first power receiving current ir1rp are in opposite phase, and the second power transmitting current it2 and the second power receiving current ir2rp are in opposite phase.

[0074] 2A , when a first power transmitting current (first AC current) it1 flows through the first power transmitting coil 2411, a first AC magnetic field is generated in accordance with the first power transmitting current it1. When the first power receiving coil 3111 is close to the first power transmitting coil 2411, the first power transmitting coil 2411 and the first power receiving coil 3111 form a first magnetic field resonance coupling. As a result, a first power receiving current ir1 flows through the first power receiving coil 3111, and wireless power feeding from the power transmitting device 20 to the first power receiving device 31 described above is realized.

[0075] 2A , when a second power transmitting current (second AC current) it2 flows through the second power transmitting coil 2421, a second AC magnetic field corresponding to the second power transmitting current it2 is generated. When the second power receiving coil 3121 is close to the second power transmitting coil 2421, the second power transmitting coil 2421 and the second power receiving coil 3121 form a second magnetic field resonance coupling. As a result, a second power receiving current ir2 flows through the second power receiving coil 3121, and wireless power feeding from the power transmitting device 20 to the second power receiving device 32 described above is realized.

[0076] 2B , when a first power transmitting current (first AC current) it1 flows through the first power transmitting coil 2411, a first AC magnetic field is generated in accordance with the first power transmitting current it1. When the first power receiving coil 3111 is close to the first power transmitting coil 2411, the first power transmitting coil 2411 and the first power receiving coil 3111 form a first magnetic field resonance coupling. As a result, a first power receiving current ir1rp flows through the first power receiving coil 3111, and wireless power feeding from the power transmitting device 20 to the first power receiving device 31 described above is realized.

[0077] 2B , when a second power transmitting current (second AC current) it2 flows through the second power transmitting coil 2421, a second AC magnetic field corresponding to the second power transmitting current it2 is generated. When the second power receiving coil 3121 is close to the second power transmitting coil 2421, the second power transmitting coil 2421 and the second power receiving coil 3121 form a second magnetic field resonance coupling. As a result, a second power receiving current ir2rp flows through the second power receiving coil 3121, and wireless power feeding from the power transmitting device 20 to the second power receiving device 32 described above is realized.

[0078] Here, the first power transmission current it1 and the second power transmission current it2 are in opposite phases, so the magnetic fields generated by the first power transmission coil 2411 and the second power transmission coil 2421 are in opposite phases.

[0079] Therefore, the first power transmitting near-field leakage magnetic flux leaking from the first power transmitting coil 2411 and the second power transmitting near-field leakage magnetic flux leaking from the second power transmitting coil 2421 have opposite phases. As a result, the first power transmitting near-field leakage magnetic flux and the second power transmitting near-field leakage magnetic flux cancel each other out in the near fields between the first power transmitting coil 2411 and the second power transmitting coil 2421. This allows the wireless power transfer system apparatus 10 to significantly suppress electromagnetic interference between the first power transmitting coil 2411 and the second power transmitting coil 2421.

[0080] FIG. 3 is a diagram illustrating an example of the state of the electromagnetic field in the far field of two power transmitting coils.

[0081] 3 , when the first power transmission current (first AC current) it1 flowing through the first power transmission coil 2411 and the second power transmission current (second AC current) it2 flowing through the second power transmission coil 2421 are in opposite phases, the electric field of the first power transmission far-field electromagnetic waves due to the first power transmission current it1 and the electric field of the second power transmission far-field electromagnetic waves due to the second power transmission current it2 are in opposite phases. Furthermore, the magnetic field of the first power transmission far-field electromagnetic waves due to the first power transmission current it1 and the second power transmission far-field electromagnetic waves and the magnetic field due to the second power transmission current it2 are in opposite phases.

[0082] Therefore, the first power transmission far-field electromagnetic waves and the second power transmission far-field electromagnetic waves cancel each other out in the far fields of the first power transmission coil 2411 and the second power transmission coil 2421. This allows the wireless power supply system apparatus 10 to suppress radiation noise from the first power transmission coil 2411 and the second power transmission coil 2421.

[0083] (Action and effect on the power receiving device 30 side) (When the first power transmitting current it1 and the first power receiving current ir1 are in phase, and when the second power transmitting current it2 and the second power receiving current ir2 are in phase) When the degree of coupling between the first power transmitting coil 2411 and the first power receiving coil 3111 is the same as the degree of coupling between the second power transmitting coil 2421 and the second power receiving coil 3121, the phase relationship between the first power receiving current ir1 due to the first power transmitting current it1 and the second power receiving current ir2 due to the second power transmitting current it2 is the same as the phase relationship between the first power transmitting current it1 and the second power transmitting current it2. Here, the first power receiving current ir1 is a current obtained by coupling the first power receiving coil 3111 to the first electromagnetic resonant field, and the second power receiving current ir2 is a current obtained by coupling the second power receiving coil 3121 to the second electromagnetic resonant field.

[0084] Therefore, as shown in FIG. 2A, if the first transmission current it1 and the second transmission current it2 are in opposite phase, the first receiving current ir1 and the second receiving current ir2 are in opposite phase.

[0085] (When the first transmitting current it1 and the first receiving current ir1rp are in opposite phases, and the second transmitting current it2 and the second receiving current ir2rp are in opposite phases) When the degree of coupling between the first transmitting coil 2411 and the first receiving coil 3111 is the same as the degree of coupling between the second transmitting coil 2421 and the second receiving coil 3121, the phase relationship between the first receiving current ir1rp due to the first transmitting current it1 and the second receiving current ir2rp due to the second transmitting current it2 is the same as the phase relationship between the first transmitting current it1 and the second transmitting current it2. Here, the first receiving current ir1rp is a current obtained by coupling the first receiving coil 3111 to the first electromagnetic resonant field, and the second receiving current ir2rp is a current obtained by coupling the second receiving coil 3121 to the second electromagnetic resonant field.

[0086] Therefore, as shown in FIG. 2B, if the first transmission current it1 and the second transmission current it2 are in opposite phases, the first receiving current ir1rp and the second receiving current ir2rp are in opposite phases.

[0087] Therefore, the magnetic field generated by the first power receiving coil 3111 and the magnetic field generated by the second power receiving coil 3121 are in opposite phases. Therefore, the first power receiving near-field leakage magnetic flux leaking from the first power receiving coil 3111 and the second power receiving near-field leakage magnetic flux leaking from the second power receiving coil 3121 are in opposite phases.

[0088] As a result, the first power receiving near-field leakage magnetic flux and the second power receiving near-field leakage magnetic flux cancel each other out in the near fields between the first power receiving coil 3111 and the second power receiving coil 3121. This allows the wireless power supply system apparatus 10 to significantly suppress electromagnetic interference between the first power receiving coil 3111 and the second power receiving coil 3121.

[0089] Furthermore, when the first power receiving current ir1 flowing through the first power receiving coil 3111 and the second power receiving current ir2 flowing through the second power receiving coil 3121 are in opposite phase, the electric field of the first power receiving far-field electromagnetic waves due to the first power receiving current ir1 and the electric field of the second power receiving far-field electromagnetic waves due to the second power receiving current ir2 are in opposite phase. Furthermore, the magnetic field of the first power receiving far-field electromagnetic waves due to the first power receiving current and the second power receiving far-field electromagnetic waves and magnetic field due to the second power receiving current are in opposite phase.

[0090] Similarly, when the first power receiving current ir1rp flowing through the first power receiving coil 3111 and the second power receiving current ir2rp flowing through the second power receiving coil 3121 are in opposite phase, the electric field of the first power receiving far-field electromagnetic waves due to the first power receiving current ir1rp and the electric field of the second power receiving far-field electromagnetic waves due to the second power receiving current ir2rp are in opposite phase. Furthermore, the magnetic field of the first power receiving far-field electromagnetic waves due to the first power receiving current and the magnetic field of the second power receiving far-field electromagnetic waves due to the second power receiving current are in opposite phase.

[0091] Therefore, the first power receiving far-field electromagnetic waves and the second power receiving far-field electromagnetic waves cancel each other out in the far fields of the first power receiving coil 3111 and the second power receiving coil 3121. This allows the wireless power supply system apparatus 10 to suppress radiation noise from the first power receiving coil 3111 and the second power receiving coil 3121.

[0092] (Example of Overall Effects) As described above, in the near-field where the distance is short, the two transmitting coils suppress electromagnetic interference, and in the far-field where the distance is long, the two transmitting coils cancel out the unwanted electromagnetic waves generated by each other, thereby suppressing the generation of unwanted electromagnetic waves. Similarly, in the near-field where the distance is short, the two receiving coils suppress electromagnetic interference, and in the far-field where the distance is long, the two receiving coils cancel out the unwanted electromagnetic waves generated by each other, thereby suppressing the generation of unwanted electromagnetic waves.

[0093] Therefore, the wireless power supply system apparatus 10 can suppress the generation of unnecessary electromagnetic waves by canceling out unwanted electromagnetic waves generated by the two power transmitting coils and by canceling out unwanted electromagnetic waves generated by the two power receiving coils. As a result, the wireless power supply system apparatus 10 can suppress undesired electromagnetic interference between the two power transmitting coils, undesired electromagnetic interference between the two power receiving coils, and radiated noise from the two power transmitting coils and two power receiving coils, thereby achieving power supply with even lower loss.

[0094] In this embodiment, a configuration consisting of two transmitting coils and two receiving coils is shown, but if there are multiple transmitting coils and multiple receiving coils, the configuration of this embodiment can be applied to achieve the same effects.

[0095] (Relationship between the distance between the transmitting coil and the receiving coil and the resonant frequency) Fig. 4(A) is a graph showing an example of the relationship between frequency and input impedance. Fig. 4(B) is a graph showing an example of the relationship between frequency and voltage gain. dx shown in Fig. 4(A) and Fig. 4(B) represents the distance between the transmitting coil and the receiving coil.

[0096] When an electromagnetic resonance field is used, wireless power transfer is possible even if the distance between the power transmitting coil and the power receiving coil is relatively long.

[0097] On the other hand, as shown in Figures 4A and 4B, when the distance between the power transmitting coil and the power receiving coil changes, the resonant frequency also changes. For example, when the distance between the power transmitting coil and the power receiving coil decreases, the resonant frequency changes from one to two. In other words, the frequency at which the input impedance is minimum changes from one to two.

[0098] When there is only one resonant frequency, the resonant frequency is the natural resonant frequency fr of the power transmitting coil and the power receiving coil. At this natural resonant frequency fr, the voltage gain of wireless power transfer becomes the highest.

[0099] Therefore, when there is one resonant frequency, the capacitance of the first power transmitting resonant capacitor 2412 and the capacitance of the second power transmitting resonant capacitor 2422 are set based on the natural resonant frequency fr.

[0100] On the other hand, when there are two resonant frequencies, the two resonant frequencies appear on the high frequency side and the low frequency side with respect to the natural resonant frequency fr.

[0101] On the other hand, when there are two resonant frequencies, the capacitance of the first power transmitting resonant capacitor 2412 and the capacitance of the second power transmitting resonant capacitor 2422 are set based on the resonant frequency on the low frequency side or the resonant frequency on the high frequency side.

[0102] For example, when the distance between the first power transmitting coil 2411 and the first power receiving coil 3111 and the distance between the second power transmitting coil 2421 and the second power receiving coil 3121 is dx=0.2, the capacitance of the first power transmitting resonant capacitor 2412 and the capacitance of the second power transmitting resonant capacitor 2422 are set based on the low-frequency resonant frequency frLB or the high-frequency resonant frequency frHB. Also, when dx=0.1, the capacitance of the first power transmitting resonant capacitor 2412 and the capacitance of the second power transmitting resonant capacitor 2422 are set based on the low-frequency resonant frequency frLA or the high-frequency resonant frequency frHA.

[0103] By setting the capacitance in this way, it is possible to set an optimum capacitance depending on the degree of coupling between the power transmitting coil and the power receiving coil.

[0104] In this case, if a resonant frequency on the low frequency side is used, the capacitances constituting the first power transmitting resonant circuit 241 and the second power transmitting resonant circuit 242 are set to be large, thereby suppressing the influence of variations in capacitance.

[0105] On the other hand, by using a resonant frequency on the high frequency side, the capacitances constituting the first power transmitting resonant circuit 241 and the second power transmitting resonant circuit 242 can be set small. This allows the first power transmitting resonant capacitor 2412 and the second power transmitting resonant capacitor 2422 to be miniaturized, thereby enabling the power transmitting device 20 to be miniaturized. Furthermore, the power transmitting device 20 can achieve soft switching or zero voltage switching operation using high frequency resonance phenomena, thereby reducing switching loss and electromagnetic interference noise. Furthermore, by using a resonant frequency on the high frequency side, an electric wall is formed between the power transmitting coil and the power receiving coil, thereby suppressing undesired electrical coupling.

[0106] The distance between the power transmitting coil and the power receiving coil can be determined, for example, by the physical shape of the power transmitting device 20 and the physical shape of the power receiving device 30. Therefore, the distance between the power transmitting coil and the power receiving coil can be set based on the physical shape of the power transmitting device 20 and the physical shape of the power receiving device 30, and the capacitance of the first power transmitting resonant capacitor 2412 and the capacitance of the second power transmitting resonant capacitor 2422 can be set based on this distance.

[0107] (Adjustment of Phase Difference Based on Distance Between First Power Transmission Coil 2411 and Second Power Transmission Coil 2421) Fig. 5 is a graph showing an example of the relationship between the distance between the first power transmission coil 2411 and the second power transmission coil 2421 and the coupling coefficient. As shown in Fig. 5, when the distance between the first power transmission coil 2411 and the second power transmission coil 2421 changes, the coupling coefficient between the first power transmission coil 2411 and the second power transmission coil 2421 changes.

[0108] Therefore, the power transmitting device 20 adjusts the phase difference between the first AC current and the second AC current in accordance with the change in the coupling coefficient (change in the distance).

[0109] More specifically, when the distance between the first power transmitting coil 2411 and the second power transmitting coil 2421 is long and the coupling coefficient is low (approximately 0), the phase difference between the first AC current and the second AC current is set to 180° (opposite phase). Then, the phase difference between the first AC current and the second AC current is set so as to approach 0° from 180° as the distance between the first power transmitting coil 2411 and the second power transmitting coil 2421 decreases. In other words, the phase difference between the first AC current and the second AC current is set so as to approach 0° from 180° as the coupling coefficient between the first power transmitting coil 2411 and the second power transmitting coil 2421 approaches 1 from 0.

[0110] By adjusting the phase difference in this manner, the wireless power supply system device 10 can set the phase difference between the first AC current and the second AC current to an optimal value depending on the distance (coupling coefficient) between the first power transmission coil 2411 and the second power transmission coil 2421.

[0111] This allows the wireless power supply system apparatus 10 to achieve wireless power supply that is more suitable for the distance (coupling coefficient) between the first power transmitting coil 2411 and the second power transmitting coil 2421.

[0112] The frequencies of the first and second AC currents are preferably in the 6.78 MHz or 13.56 MHz band of the ISM band, which is a wireless communication frequency band allocated for general use in the medical, industrial, and scientific fields.

[0113] Second Embodiment A wireless power supply system according to a second embodiment of the present invention will be described with reference to the drawings. Fig. 6 is an equivalent circuit diagram of the wireless power supply system according to the second embodiment of the present invention.

[0114] 6 , the wireless power supply system apparatus according to the second embodiment differs from the wireless power supply system apparatus 10 according to the first embodiment in that it includes a power transmitting device 20A. Below, the differences between the wireless power supply system according to the second embodiment and the wireless power supply system apparatus 10 according to the first embodiment will be described, and a description of the similarities will be omitted.

[0115] The power transmitting device 20A differs from the power transmitting device 20 according to the first embodiment in that it includes an MCU 21A, a current detection circuit 251, and a current detection circuit 252.

[0116] The current detection circuit 251 detects a change over time in the phase of the first AC current it1A flowing through the first power transmitting coil 2411. The current detection circuit 251 outputs the change over time in the phase of the first AC current it1A to the MCU 21A.

[0117] The current detection circuit 252 detects a change over time in the phase of the second AC current it2A flowing through the second power transmitting coil 2421. The current detection circuit 252 outputs the change over time in the phase of the second AC current it2A to the MCU 21A.

[0118] The MCU 21A detects the phase difference between the first AC current it1A and the second AC current it2A based on the time change in the phase of the first AC current it1A and the time change in the phase of the second AC current it2A.

[0119] For example, the distance between the first power transmitting coil 2411 and the second power transmitting coil 2421 is known if the shape of the power transmitting device 20A is known. Therefore, the distance between the first power transmitting coil 2411 and the second power transmitting coil 2421, i.e., the phase difference that is optimal for the coupling coefficient between the first power transmitting coil 2411 and the second power transmitting coil 2421, is also known. The MCU 21A compares the detected phase difference with the optimal phase difference. The MCU 21A adjusts the power transmitting control signal to achieve the optimal phase difference, and outputs the adjusted signal to the first switching control circuit 221 and the second switching control circuit 222.

[0120] This allows the power transmission device 20A to feedback and set the phase difference between the first AC current and the second AC current to an optimal value according to the distance (coupling coefficient) between the first power transmission coil 2411 and the second power transmission coil 2421.

[0121] In the above description, the positional relationship between the first power transmitting coil 2411 and the second power transmitting coil 2421 is fixed. However, even in cases where the positional relationship between the first power transmitting coil 2411 and the second power transmitting coil 2421 is changeable, the above-described feedback setting of the phase difference can be applied.

[0122] [Third Embodiment] A wireless power supply system apparatus according to a third embodiment of the present invention will be described with reference to the drawings. Fig. 7 is an equivalent circuit diagram of the wireless power supply system apparatus according to the third embodiment of the present invention.

[0123] 7 , the wireless power supply system apparatus according to the third embodiment differs from the wireless power supply system apparatus 10 according to the first embodiment in that it includes a power transmitting apparatus 20B. Below, differences between the wireless power supply system according to the third embodiment and the wireless power supply system apparatus 10 according to the first embodiment will be described, and descriptions of similarities will be omitted.

[0124] The power transmitting device 20B differs from the power transmitting device 20 according to the first embodiment in that it includes an MCU 21B, a current detection circuit 251, a current detection circuit 252, a first power transmitting resonant capacitor 2412B, and a second power transmitting resonant capacitor 2422B.

[0125] The first power transmitting resonant capacitor 2412B and the second power transmitting resonant capacitor 2422B are configured as variable capacitors.

[0126] The current detection circuit 251 detects the current value of the first AC current it1B flowing through the first power transmitting coil 2411. The current detection circuit 251 outputs the current value of the first AC current it1A to the MCU 21B.

[0127] The current detection circuit 252 detects the current value of the second AC current it2B flowing through the second power transmitting coil 2421. The current detection circuit 252 outputs the current value of the second AC current it2B to the MCU 21B.

[0128] The MCU 21B estimates the input impedance seen from the first power conversion circuit 231 to the load 341 based on the current value of the first AC current it1B. The MCU 21B estimates the input impedance seen from the second power conversion circuit 232 to the load 342 based on the current value of the second AC current it2B.

[0129] The MCU 21B also stores the current capacitance of the first power transmitting resonant capacitor 2412B and the current capacitance of the second power transmitting resonant capacitor 2422B, thereby enabling the MCU 21B to estimate the frequency characteristics of the current input impedance.

[0130] MCU21B estimates the distance between the first transmitting coil 2411 and the first receiving coil 3111, and the distance between the second transmitting coil 2421 and the second receiving coil 3121 based on the frequency characteristics of the estimated current input impedance and the input impedance estimated based on the current value.

[0131] The MCU 21B estimates the frequency at which the input impedance is at a minimum based on the estimated distance, and adjusts the capacitance of the first power transmitting resonant capacitor 2412B and the capacitance of the second power transmitting resonant capacitor 2422B so that the frequency at which the estimated input impedance is at a minimum is substantially the same as the resonant frequency.

[0132] This allows the power transmission device 20B to set the capacitance of the first power transmitting resonant capacitor 2412B by feedback to an optimal value according to the distance between the first power transmitting coil 2411 and the first power receiving coil 3111. Furthermore, the power transmission device 20B can set the capacitance of the second power transmitting resonant capacitor 2422B by feedback to an optimal value according to the distance between the second power transmitting coil 2421 and the second power receiving coil 3121.

[0133] <1> A wireless power transmitter including a first power transmitting coil and a second power transmitting coil, comprising: a first power transmitting resonant circuit configured using the first power transmitting coil and a first power transmitting resonant capacitor; a second power transmitting resonant circuit configured using the second power transmitting coil and a second power transmitting resonant capacitor; a first power conversion circuit that converts an input DC voltage into an AC current by a switching operation and supplies the AC current to the first power transmitting coil; a second power conversion circuit that converts the input DC voltage into an AC current by a switching operation and supplies the AC current to the second power transmitting coil; a first switching control circuit that controls the switching operation of the first power conversion circuit; and a second switching control circuit that controls the switching operation of the second power conversion circuit, wherein the first switching control circuit and the second switching control circuit perform power transmission control such that a phase of a first AC current flowing through the first power transmitting coil and a phase of a second AC current flowing through the second power transmitting coil are opposite phases, a wireless power transmission device in which the first power transmission resonant capacitor and the second power transmission resonant capacitor have capacitance values ​​set so that, at a switching frequency, an input impedance viewed from the first power transmission coil and the second power transmission coil toward a load to which the wireless power transmission device supplies power is near a minimum; a first electromagnetic resonant field by the first power transmission coil and a second electromagnetic resonant field by the second power transmission coil are individually formed; in a near field where the distance to the first power transmission coil and the second power transmission coil is short, the first power transmission coil and the second power transmission coil are arranged at a distance to suppress electromagnetic interference between the first power transmission coil and the second power transmission coil; and in a far field where the distance to the first power transmission coil and the second power transmission coil is long, the electromagnetic waves generated by the first power transmission coil and the electromagnetic field generated by the second power transmission coil cancel each other out.

[0134] <2> The wireless power transmitting device according to <1>, further comprising a power transmission control circuit that sets a phase to be controlled by the first switching control circuit and the second switching control circuit, wherein the power transmission control circuit: sets an opposite phase when a coupling coefficient between the first power transmitting coil and the second power transmitting coil is 0; and sets a magnitude of a phase difference relative to the opposite phase in accordance with a magnitude of the coupling coefficient when the coupling coefficient between the first power transmitting coil and the second power transmitting coil is greater than 0 and equal to or less than 1.

[0135] <3> The wireless power transmitting device according to <2>, wherein the power transmission control circuit sets the phase difference so that it approaches 0° from 180° as the coupling coefficient approaches 1 from 0.

[0136] <4> The wireless power transmitting device according to <2> or <3>, further comprising a coupling coefficient setting circuit that sets the coupling coefficient, wherein the power transmission control circuit sets the phase difference based on the coupling coefficient set by the coupling coefficient setting circuit.

[0137] <5> The wireless power transmission device according to any one of <1> to <4>, wherein the input impedance has a characteristic of having a minimum value at a switching frequency that forms the first electromagnetic resonant field and the second electromagnetic resonant field, and the capacitance of the first power transmission resonant capacitor and the capacitance of the second power transmission resonant capacitor are set to capacitances that operate on the low-frequency side of the minimum value of the input impedance.

[0138] <6> The wireless power transmission device according to any one of <1> to <4>, wherein the input impedance has a characteristic of having a minimum value at a switching frequency that forms the first electromagnetic resonant field and the second electromagnetic resonant field, and the capacitance of the first power transmission resonant capacitor and the capacitance of the second power transmission resonant capacitor are set to capacitances that operate on the high-frequency side of the minimum value of the input impedance.

[0139] <7> The wireless power transmitting device according to any one of <1> to <6>, wherein the first power transmitting coil and the second power transmitting coil have the same size.

[0140] <8> The wireless power transmitting device according to any one of <1> to <7>, wherein a switching frequency is in the 6.78 MHz band or the 13.56 MHz band of the ISM band, and a frequency of the AC current flowing through the first power transmitting coil is in the 6.78 MHz band or the 13.56 MHz band.

[0141] 10: Wireless power supply system apparatus 20, 20A, 20B: Power transmission device 21, 21A, 21B: MCU 221: First switching control circuit 222: Second switching control circuit 231: First power conversion circuit 232: Second power conversion circuit 241: First power transmission resonant circuit 242: Second power transmission resonant circuit 251, 252: Current detection circuit 2411: First power transmission coil 2412, 2412B: First power transmission resonant capacitor 2421: Second power transmission coil 2422, 2422B: Second power transmission resonant capacitor 30: Power receiving device 31: First power receiving device 32: Second power receiving device 321: First power receiving rectifier circuit 322: Second power receiving rectifier circuit 331: First power receiving smoothing circuit 332: Second power receiving smoothing circuit 341, 342: Load 3111: First power receiving coil 3121: Second power receiving coil 3112: First power receiving resonant capacitor 3122: Second power receiving resonant capacitor S1H, S1L, S2H, S2L: Switching elements

Claims

1. A wireless power transmission device comprising a first power transmission coil and a second power transmission coil, comprising: a first power transmission resonant circuit configured using the first power transmission coil and a first power transmission resonant capacitor; a second power transmission resonant circuit configured using the second power transmission coil and a second power transmission resonant capacitor; a first power conversion circuit that converts an input DC voltage into an AC current by switching operation and supplies the AC current to the first power transmission coil; a second power conversion circuit that converts the input DC voltage into an AC current by switching operation and supplies the AC current to the second power transmission coil; a first switching control circuit that controls the switching operation of the first power conversion circuit; and a second switching control circuit that controls the switching operation of the second power conversion circuit, wherein the first switching control circuit and the second switching control circuit perform power transmission control such that the phase of the first AC current flowing through the first power transmission coil and the phase of the second AC current flowing through the second power transmission coil are opposite phases; a wireless power transmitting device in which the first power transmitting resonant capacitor and the second power transmitting resonant capacitor have capacitance values ​​set so that, at a switching frequency, an input impedance viewed from the first power transmitting coil and the second power transmitting coil toward a load to which the wireless power transmitting device supplies power is near a minimum; a first electromagnetic resonant field by the first power transmitting coil and a second electromagnetic resonant field by the second power transmitting coil are individually formed; in a near field where the distance to the first power transmitting coil and the second power transmitting coil is short, the first power transmitting coil and the second power transmitting coil are arranged at a distance to suppress electromagnetic interference between the first power transmitting coil and the second power transmitting coil; and in a far field where the distance to the first power transmitting coil and the second power transmitting coil is long, the electromagnetic waves generated by the first power transmitting coil and the electromagnetic field generated by the second power transmitting coil cancel each other out.

2. A wireless power transmission device as described in claim 1, comprising a power transmission control circuit that sets the phases controlled by the first switching control circuit and the second switching control circuit, wherein the power transmission control circuit sets the phase to be opposite when the coupling coefficient between the first power transmission coil and the second power transmission coil is 0, and sets the magnitude of the phase difference relative to the opposite phase according to the magnitude of the coupling coefficient when the coupling coefficient between the first power transmission coil and the second power transmission coil is greater than 0 and equal to or less than 1.

3. The wireless power transmitting device according to claim 2, wherein the power transmission control circuit sets the phase difference to approach 0° from 180° as the coupling coefficient approaches 1 from 0.

4. A wireless power transmission device according to claim 2 or claim 3, further comprising a coupling coefficient setting circuit that sets the coupling coefficient, and wherein the power transmission control circuit sets the phase difference based on the coupling coefficient set by the coupling coefficient setting circuit.

5. A wireless power transmission device according to any one of claims 1 to 4, wherein the input impedance has a characteristic of having a minimum value at a switching frequency that forms the first electromagnetic resonant field and the second electromagnetic resonant field, and the capacitance of the first power transmission resonant capacitor and the capacitance of the second power transmission resonant capacitor are set to capacitances that operate on the low-frequency side of the minimum value of the input impedance.

6. A wireless power transmission device according to any one of claims 1 to 4, wherein the input impedance has a characteristic of having a minimum value at a switching frequency that forms the first electromagnetic resonant field and the second electromagnetic resonant field, and the capacitance of the first power transmission resonant capacitor and the capacitance of the second power transmission resonant capacitor are set to capacitances that operate on the high-frequency side of the minimum value of the input impedance.

7. The wireless power transmission device according to any one of claims 1 to 6, wherein the first power transmission coil and the second power transmission coil have the same size.

8. A wireless power transmitting device according to any one of claims 1 to 7, wherein the switching frequency is in the 6.78 MHz band or 13.56 MHz band of the ISM band, and the frequency of the AC current flowing through the first power transmitting coil is in the 6.78 MHz band or 13.56 MHz band.

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